Rotary electric machine

Abstract: Disclosed is a rotary electric machine, such as an alternating current generator for vehicles, which can increase cooling flow quantity and reduce whizzing sound. In this rotary electric machine, cooling wind blown from a centrifugal fan (6, 60) flows into a numerosity of cooling windows (w) which surround the centrifugal fan (6, 60). The cooling windows (w) are separated in the circumferential direction by support parts (8) or guide wall parts (7). The angle (ϑ) of inclination of the guide wall part (7) against the radial direction is set to be larger in the vicinity of the forward end (a) of the support part (8) in the rotating direction and smaller in the vicinity of the backward end (b) of the support part (8) in the rotating direction to increase the cooling flow quantity. Furthermore, the circumferential widths (H) of the cooling windows (w) are set to be narrower in the vicinity of the support part (8) and wider in the distance from the support part (8) to increase the cooling flow quantity. Moreover, the axial length of the cooling window (w) is set to become gradually longer from the vicinity of the support part (8) towards the intermediate area between the support parts (8).

Description: BACKGROUND OF THE INVENTION The present invention generally relates to a rotary electric machine such as an alternating current generator for vehicles and, more particularly, to a cooling mechanism of such rotary electric machine. As an example of conventional rotary electric machines, Japanese Unexamined Patent Publication No. 3-178593 discloses an alternating current generator as illustrated in Fig. 8 and corresponding to the preamble of claim 1. This alternating current generator includes a housing 100 with a plurality of cooling windows w opened in a cylindrical peripheral wall thereof in circumferential alignment, and a centrifugal fan 106 positioned inside the cooling windows w and fixed to the end of a rotor (not illustrated) in the housing 100. The peripheral wall of the housing 100 has guide wall parts 102, each of which is positioned between circumferentially adjacent two of the cooling windows w and extends axially. Each guide wall part 102 is inclined at a constant angle  against the radial direction, so that the cooling wind blown out of the cooling windows w is blown out in this inclined direction. Between the two circumferentially adjacent cooling windows w, support parts 103 extend axially and the circumferential width of each support part 103 is made to be wider than the circumferential width of the guide wall part 102. In the above conventional rotary electric machine, the support parts 103 result in large fluid resistances against cooling wind generated by the centrifugal fan 106, causing increase in fluid loss, decrease in cooling ability or increase in whizzing sound. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problem by providing a rotary electric machine which can increase the cooling flow quantity without any further addition of power. It is a further object of the present invention to reduce whizzing sound in the rotary electric machine. According to one aspect of a rotary electric machine according to the present invention, angle of inclination of guide wall parts formed on a periphery of a cylindrical housing against the radial direction is set to be larger in the vicinity of the forward end of each support part in rotating direction and smaller in the vicinity of the backward end of the support part in the rotating direction. Preferably, the angle of inclination of the guide wall parts is set to become gradually smaller from the vicinity of the forward end of the support part in the rotating direction torwards the vicinity of the backward end of the support part in the rotating direction, whereby the cooling flow quantity can be increased and whizzing sound can be reduced. More preferably, chord direction (blade length direction) of the guide wall parts is in the same direction as that of the cooling wind flowing into the cooling windows at the rotational speed at which the temperature of the blown air is the highest in a full-load operation. Thus fluid resistance at the guide wall parts under the worst conditions can be minimized, and the cooling flow quantity can be increased under the worst conditions. That is, the worst heat load in the rotary electric machine is generated in the preset rotational speed range in a full-load operation. In other words, the electric generating power, the internal radiating resistance and the cooling flow quantity vary according to the rotational speed, and the difference (internal temperature rise) between the internal heat generation quantity and heat radiation quantity (which can be generally regarded as the cooling flow quantity) is the largest within the preset rotational speed range. Still more preferably, the cooling windows are formed on the housing to extend from the peripheral wall of the housing to the end part thereof in the axial direction. Thus a plurality of cooling windows can deliver the cooled air more smoothly. According to the other aspect of the rotary electric machine according to the present invention, circumferential width of the cooling windows is set to be wider in the intermediate area between the adjacent two support parts than in the vicinity of said support parts. Preferably, the circumferential width of the plurality of cooling windows is set to become gradually larger from the vicinity of each support part toward the intermediate area between the adjacent two support parts. Thus, the circumferential width of each cooling window can almost match with the flow quantity therethrough, whereby the fluid resistance can be further reduced and whizzing noise is further reduced. More preferably, the axial length of the cooling windows is set to be longer in the intermediate area between the adjacent support parts than any other area. Thus the increase in the fluid resistance can be controlled, the noise generated within the housing can effectively be shut off, and the strength around the support parts can be increased. By setting the axial length of the plurality of cooling windows to become gradually longer from the vicinity of each support part to the intermediate area between the adjacent support parts, the axial length of each cooling window can match with the flow quantity therethrough. Alternatively, the axial length of the plurality of cooling windows may be set to be equal so that the mechanism can be simplified and the cooling flow quantity can be increased. According to the above characteristic features, cooling wind blown from the centrifugal fan flows in the direction of inclination of the guide parts against the radial and circumferential directions. However, the wind that bumps the support part is bent thereby in the circumferential direction, and as a result, the component of wind velocity in the circumferential direction in the vicinity of the forward end of the support in the rotating direction increases by the addition of the cooling wind that bumped the support part and was bent thereby in the circumferential direction. Accordingly, the fluid resistance at the guide wall part can be reduced, the effect of flow control can be improved, and the cooling flow quantity can be increased. Further, the fluid resistance to the cooling wind blown from the centrifugal fan is large in the vicinity of the support part due to the interruption by the support parts and small in the intermediate area between the support parts due to the concentration of a numerosity of cooling windows therein. The quantity of the wind blown from the cooling window is small in the vicinity of the support part and large in the distance from the support part. Accordingly, overall fluid resistance is appropriately reduced and the cooling flow quantity can be increased. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is a cross-sectional view illustrating an alternating current generator for vehicles according to the first embodiment of the present invention; Fig. 2 is a front view viewed from the rear side of the generator of Fig. 1 with a cover and electric components removed therefrom; Fig. 3 is a diagram illustrating the layout of the blades of a rear side fan; Fig. 4 is a characteristic diagram illustrating the relation among the flow quantity, direction and the circumferential angle position of the cooling wind blown out of the cooling windows of the generator of Fig. 1; Fig. 5 is a characteristic diagram illustrating the relation between the rotational speed and the flow quantity of the cooling wind in each embodiment model; Fig. 6 is a front view illustrating the alternating current generator according to the second embodiment of the present invention viewed from the rear side of the generator with a cover and electric components removed therefrom; Fig. 7 is a side view viewed in the direction of the arrow A of Fig. 6; and Fig. 8 is a front view viewed from the rear side of a conventional generator with a cover and electric components removed therefrom. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Description will now be given to an alternating current generator for vehicles as a rotary electric machine of the present invention, referring to Figs. 1, 2 and 3. As illustrated in Fig. 1, a frame (or a generally cylindrical housing as referred to in the present invention) 1 comprises a front frame 11 and a rear frame 12 which are fastened to each other with fastening bolts 13. The frame 1 rotatably supports a rotary shaft or spindle 2 to which a field core 31 is fixed and the field core 31 is wound with a field coil 32 thereon. The field core 31 and the field coil 32 form a rotor of an alternating current generator. Inside of the frame 1, an armature core 33 circumferentially surrounding the field core 31 is fixed and the armature core 33 is wound with an armature coil 34 thereon. The armature core 33 and the armature coil 34 form a stator of the generator. An end cover 4 is fixed, covering the rear end face of the rear frame 12, and an electric component chamber S is formed between the rear frame 12 and the cover 4. The electric component chamber S houses therein a rectifier mounted by bolts 10, a brush and a regulator (these components being not illustrated). When the spindle 2 is belt-driven by an engine through a pulley 21 and, at the same time, the field coil 32 is electrically energized for excitation, a three-phase alternating current (AC) voltage generated in the armature coil 34 is subjected to three-phase full-wave rectification by the rectifier and then outputted for charging a battery. The characteristic parts of this embodiment will now be described with reference to a cross-sectional view of Fig. 1 and a front view of Fig 2 illustrating an end surface of the rear frame 12 with the cover 4 removed therefrom. Fixed to the spindle 2 for rotation therewith and generation of cooling wind thereby are an inclined flow fan 5 and a centrifugal fan 6 sandwiching the field core 31 therebetween. Around the peripheral wall of the front frame 11 are a numerosity of cooling windows w' opened in a circumferential alignment. On the other hand, around the peripheral wall of the rear frame 12 are a plurality of cooling windows w opened in a circumferential alignment encompassing blades 60 of the centrifugal fan 6. Part of the wind generated by the inclined flow fan 5 is blown out of the cooling windows w', and the remaining part of the same wind is flowed axially along the outer periphery of the field core 31 to the rear side and then blown out of the cooling windows w in centrifugal directions. Each blade 60 of the centrifugal fan 6 is positioned at irregular pitches or angular spaces as illustrated in Fig. 3, i.e., four blades are positioned at a pitch a1, another four blades at a pitch a2, and the remaining three blades at a pitch a3, wherein a1 < a2 < a3. The wind generated by the centrifugal fan 6 is blown out of the cooling windows w in centrifugal directions. The peripheral area of the cooling windows w will now be described with reference to Fig. 2. Each of cooling windows w is provided between circumferentially adjacent two guide wall parts 7 as a circumferential border to define the direction of the wind blowing out of the cooling windows w. The guide wall parts 7 are integrally cast with the rear frame 12 to be a flat plate with the inner peripheral end part (blade front tip part) and the outer peripheral end (blade rear tip part) rounded. Here, the dimension between the inner peripheral end (blade front tip end) and the outer peripheral end (blade rear tip end) is called as chord length or blade length. Both the principal planes of the guide wall parts 7 are parallel with each other in the axial direction and almost flat planes inclined against the radial and circumferential directions. Accordingly, between two adjacent guide wall parts 7 is the cooling window w, and the circumferential width H of each cooling windows w is measured at right angles to the mean angle m of the angles L and F {=(L+F)/2} between the chord direction G and radial direction R of the two adjacent guide wall parts 7 contacting the cooling window w. Here, each chord direction G is the mean value of the angles of inclination of both the principal planes of the guide wall part 7 facing each other. Formed between some of the two cooling windows w circumferentially adjacent to each other are support parts 8. The support parts 8 are provided at five locations at intervals in the circumferential direction. The circumferential width thereof is set to 2 to 5 times as wide as the sum of the circumferential widths of one guide wall 7 and one cooling window w. As illustrated in Figs. 1 and 2, the support parts 8 are disposed beneath the fastening bolts 13 and one support part 8 in the supporting position for a stay 3. Bolt holes 14 through which the fastening bolts 13 are screwed in are made in ear parts 15 of the rear frame 12, the ear parts 15 being projecting in the outside diameter direction. Each ear part 15 extends in the outside diameter direction from the front end of each support parts 8. Accordingly, the support parts 8 function to transmit the fastening force of the fastening bolts 13 to the entire rear frame 12. The characteristics of this first embodiment will now be described. In this embodiment, the angle (the angle of inclination as referred to in the present invention)  between the chord direction G and radial direction R of the guide wall part 7 is set to be larger (more inclined in the circumferential or rotating direction) as the guide wall part 7 is nearer in the rotating direction to the forward end a of each support part 8 and smaller (more close to the radial direction R) as the guide wall part 7 is nearer in the rotating direction to the backward end b of each support part 8 as 1 > 2 > 3 > 4 > 5 > 6 > 7, for example. In the above arrangement, the cooling wind is blown out with slight inclination against the circumferential direction nearby the forward end of the support part 8 in the rotating direction and with slight inclination against the radial direction nearby the backward end of the support 8 in the rotating direction. In other words, the cooling wind flows with inclination against the radial and circumferential directions. However, the wind bumping the support part 8 is bent thereby to the circumferential direction, and as a result, the component of velocity of the cooling wind in the circumferential direction nearby the forward end a of the support part 8 in the rotating direction increases by the addition of the cooling wind which bumped the support part 8 and was bent thereby in the circumferential direction. In short, the wind blown out of the cooling window w is more inclined in the circumferential direction as the wind approaches the forward end a of the support part 8 in the rotating direction. As the chord direction of each guide wall part 7 is gradually varied according to the variation in the cooling wind direction caused by the support parts 8, the cooling wind bumped at the support parts 8 is easily blown out through the guide wall parts 7 near the forward end a. Thus the fluid resistance of each guide wall part 7 can be reduced, the effect of flow control can be improved, and the cooling wind flow quantity can be increased. Also in this embodiment, the circumferential width H of each cooling window w is set to be narrower in the vicinity of the support part 8 and wider in the distance from the support part 8 as H2 < H3 < H4 > H5 > H6 > H7, for example. By this arrangement, the fluid resistance to the wind blown out of the centrifugal fan 6 is large in the vicinity of the support part 8 due to the interruption by the support part 8 and small in the intermediate area between two support parts 8 due to the numerosity of cooling windows w concentratedly formed therein. In short, the flow quantity of the cooling wind blown out of the cooling window w is smaller in the vicinity of the support part 8 and larger in the distance from the support part 8. Therefore, by so arranging that the opening area of the cooling windows w in the distance from the support part 8 is larger than that in the vicinity of the support part 8, the total fluid resistance can be reduced, the difference in the velocity of the cooling wind blown out of each cooling window w can be decreased, and the cooling flow quantity can be increased. The above embodiment may be so modified that the chord direction (blade length direction) G of the guide wall part 7 is set in the direction K of the cooling wind blown into the cooling window w at the rotational speed at which the temperature of the blown air is the highest in a full-load operation (with the designed maximum allowable electric power supply). For reference, the rotational speed at which the temperature of the blown air is the highest in a full-load operation (with the designed maximum allowable electric power supply), ntmax, slightly varies according to the type of alternating current generators. In most alternators, such rotational speed ntmax ranges from 3,000 to 4,000 rpm. When the difference between the angle of inclination of the guide wall parts 7 and the inflow angle of the inflow cooling wind is 10 degrees or less, the fluid loss is small, and when the variation in the rotational speed is within a range from 0.8 to 1.2 × ntmax, the variation in the cooling wind direction is small. Therefore, when the direction of the cooling wind blown into the cooling windows w is coincided with the chord direction (blade length direction) G of the guide wall part 7 (which means that the difference between these two directions is 10 degrees or less) at a rotational speed of 0.8 to 1.2 × ntmax, the fluid resistance at the guide wall parts 7 is the smallest under the above operating condition, whereby the cooling flow quantity can be increased. Also in this modification, in case that the support part 8 is provided, the angle of inclination, etc. of the guide wall parts 7 should be varied like the first embodiment. It is to be understood that, in each of the above constructions, the whizzing sound can be reduced for a quiet operation. The results of an experiment are illustrated in Fig. 4. In this experiment, the cooling wind direction (the direction of the maximum cooling wind velocity referred to as peak angle in Fig. 4) and the cooling flow quantity both in each circumferential angle position Φ against the support part 8, using a model with all the guide wall parts 7 circumferentially dividing the cooling windows w between two support parts 8 in the upper part of Fig. 2 removed. The rotational speed was set to 3500rpm. The model used in the experiment was an alternating current generator for vehicles with a rated voltage of 12V and a rated output of 100A. The positions in the vicinity of 0° and 90° were the positions of the support parts 8. The significance and advantage of the construction of the above embodiments could be understood from Fig. 4. In Fig. 5 which shows relation between the flow quantity and the rotatioanl speed, the solid line indicates the results of the experiment on the above embodiments. The chain line with one dot indicates the results of the experiment with the angle of the guide wall part (rib) gradually changed and the window width constant. The chain line with two dots indicates the results of the experiment with the rib angle constant and the window width gradually changed. The broken line indicates the results of the experiment on only the above modified embodiment (however, with the angle of inclination of each guide wall part 7 fixed). The second embodiment will now be described with reference to Figs. 6 and 7. In this embodiment, the angle of inclination  of the guide wall parts 7 is defined as the angle LB of the wall on the backward end side of the rotating direction. Like the first embodiment, this angle LB is set to become gradually smaller from the vicinity of the forward end a of the support part 8 towards the backward end b of the support part 8 in the rotating direction. The width of the cooling window w is arranged in the same way as in the first embodiment. Fig. 7 is a side view viewed in the direction of the arrow A of Fig. 6. The axial length of cooling windows w are set to become gradually longer from the vicinity of the support parts 8 towards the intermediate area between the support parts 8. By this arrangement, the fluid resistance of each guide wall part 7 can be reduced, the effect of flow control can be improved, and the cooling flow quantity can be increased, as in the above embodiments. Particularly, the noise generated from the bottom part of the armature coil 34 within the frame 1 can be sufficiently shut off. Furthermore, when the frame 1 is manufactured by die casting, for instance, if the cooling windows w are unconditionally enlarged in an attempt to maximize the cooling ability, the guide wall parts 7 will be narrowed to the extent to be easily deformed. In particular, the guide wall parts 7 adjacent to the support parts 8 may cause the insufficient run of the molten metal due to sharp change in the width between the guide wall part and the support part 8 and the depth, resulting in insufficient strength. However, this embodiment is free from these problems, allowing very stable casting and substantial improvement in strength. In this embodiment, it is acceptable to set the axial length of each cooling windows w to be constant. For instance, in the first embodiment and its modification, it is possible to set the axial length of each cooling windows w to become gradually longer from the vicinity of the support part 8 towards the intermediate area between the support parts 8, or otherwise to be constant.

Claims: Rotary electric machine, comprising: [a] a housing (1) with a plurality of cooling windows (w) opened in a cylindrical peripheral wall thereof in circumferential alignment; [b] a stator (33, 34) fixed within said housing (1); [c] a rotor (31, 32) rotatably supported within said housing; and [d] a centrifugal fan (6) positioned inside said cooling windows (w) and fixed to one end of said rotor (31, 32); [e] the peripheral wall of said housing (1) being provided with [e1] guide wall parts (7) positioned between circumferentially adjacent two of said cooling windows (w) and extending parallel to said rotor (31, 32), thereby defining the direction of the cooling wind blown out of said cooling windows (w), and [e2] support parts (8) positioned between circumferentially adjacent two of said cooling windows (w) and extending parallel to said rotor (31, 32), the circumferential width of said support parts (8) being greater than that of said guide wall parts (7); [f] the machine being characterised in that [f1] the angle () of inclination of said guide wall parts (7) against the radial direction is set in such a way that this angle is larger in the vicinity of a forward end (a) of said support parts (8) in the rotating direction and smaller in the vicinity of a backward end (b) of said support part (8) in the rotating direction, and/or [f2] a circumferential width (H) of said cooling windows (w) is set in such a way that it is wider in an intermediate area between said support parts (8) than in the vicinity of said support parts (8). Rotary electric machine according to claim 1, wherein the angle of inclination of said guide wall parts (7) against the radial direction is set to become gradually smaller from the vicinity of the forward end (a) of said support parts (8) in the rotating direction towards the vicinity of the backward end (b) of said support parts (8) in the rotating direction. Rotary electric machine according to claim 1, wherein said guide wall parts (7) are formed in the direction of the cooling wind flowing into said cooling windows (w) at the rotational speed at which the temperature of the blown air is the highest in a full-load operation. Rotary electric machine according to claim 1, wherein the circumferential width (H) of said plurality of cooling windows (w) is set to become gradually wider from the vicinity of said support parts (8). Rotary electric machine according to one of claims 1 through 4, wherein said plurality of cooling windows (w) axially extend from the peripheral wall of said housing to the end thereof and the axial length of said cooling windows (w) is set to be longer in the intermediate area between said support parts (8) than in the vicinity of said support parts (8). Rotary electric machine according to one of claims 1 through 4, wherein said cooling windows (w) axially extend from the peripheral wall of said housing to the end thereof and the axial length of said cooling windows (w) is set to be constant. Rotary electric machine according to one of claims 1 through 6, wherein said centrifugal fan (6) includes a plurality of fan blades (60) which are circumferentially arranged with different angular spaces (a1, a2, a3).

Inventors: FUJIMOTO HIROFUMI, KONAYA KAZUYOSHI, SAKAKIBARA HIROSHI, FUJIMOTO, HIROFUMI, KONAYA, KAZUYOSHI, SAKAKIBARA, HIROSHI
Applicants: NIPPON DENSO CO, NIPPONDENSO CO., LTD.
Application year: 1994
Main classification: H02K9
IPC codes: H02K9, H02K5